An inkjet recording method has been spreading rapidly and is still being improved because of inexpensive material cost, high-speed recording, less noise during recording, and easy implementation of color recording.
The inkjet recording method includes: a continuous method which causes a droplet to continuously travel by air; and an on-demand method which causes a droplet to travel by air, depending on an image information signal. The droplet is ejected by using a pressure using a piezo element; by generation of bubbles in ink by heating; by using ultrasonic wave; or by suctioning with electrostatic force.
Examples of inkjet recording inks include water inks, oil inks, and solid (fusible) inks.
A coloring agent for use in the inkjet recording ink needs to have good solubility and dispersibility with respect to a solvent; excellent color developing ability which allows high-density recording; good hue; excellent fastness to light, heat, and active gas in the environment (NOx, acidic gas (ozone, etc.), SOx, etc.); excellent fastness to water and chemicals; good fixing ability and bleeding resistance with respect to an image receiving material; excellent preservability as ink; no toxicity; high purity; and inexpensive availability. However, it is considerably difficult to find a coloring agent meeting these criteria to a high extent. Particularly, there is a strong desire for a coloring agent for black ink which has good black tonality, allows high-density printing, and has fastness to light, humidity and heat.
Disazo dyes and trisazo dyes have been used as black dyes. When only these dyes are used, blue to green light are insufficiently absorbed, so that it is often that satisfactory black tonality is not obtained. Therefore, a color correcting dye which absorbs blue to green light is generally used in combination with the above-described dyes. Such a color correcting dye has been proposed in, for example, Japanese Unexamined Patent Publication No. H09-255906 and Japanese Patent No. 3178200 so as to make an attempt to improve black tonality adjusting ability, color developing ability, fastness, ink preservation stability, water resistance, and prevention of nozzle clogging.
However, the color correcting dye proposed in the related art has problems with the color tonality adjusting ability. Specifically, for example, it absorbs a very short wavelength, so that a large amount thereof needs to be added. Further, another color correcting dye is required.
Dyes capable of absorbing blue to green light are generally known, however, most of them have poor fastness, so that their hue may be significantly altered by exposure to light, heat, or active gas in the environment; and insufficient fixing ability, so that yellow bleeding appears at a contour portion under high temperature and high humidity conditions, for example. Therefore, a further improvement is required.
In consideration of these drawbacks, Japanese Unexamined Patent Publication No. 2002-332426 describes a black ink composition in which a triazine dye which has a maximum absorption of visible spectra in aqueous solvent at 435 nm (color correcting dye) is blended with a black dye.
However, a general black dye has a maximum absorption between 570 nm and 620 nm. Therefore, even when the color correcting dye is used, it is clear that a preferable black tonality is not obtained, taking into account a complementary color relationship which is important for adjustment of black tonality (“Shikisai Kagaku Handobukku (Handbook of Color Science) (Second Edition)”, University of Tokyo Press, 1998, pp. 560-562).
Japanese Unexamined Patent Publication No. H08-302255 describes CI Direct Red 84. However, the publication does not disclose a black ink composition in which CI Direct Red 84 is used as a short-wavelength dye in combination with a long-wavelength dye.
Japanese Unexamined Patent Publication No. 2000-265099 describes CI Direct Red 84, which is used to obtain magenta (column 8). Similarly, however, the publication does not disclose a black ink composition in which CI Direct Red 84 is used as a short-wavelength dye in combination with a long-wavelength dye.